The present invention relates to a process for treating fibrous material and more particularly to a process for inhibiting discoloration occurring when said fibrous material is heat-cured in the presence of an alkaline catalyst.
Heretofore, there have been known that treatment methods comprising heat-curing cellulosic fibrous material by using such a cross-linking agent as bis (.beta.-hydroxyethyl)sulfone, and an alkaline catalyst. When such a heat-curing treatment is carried out in the presence of the alkaline catalyst, however, the treatment is accompanied by a tendency of the fibrous material to discolor into colar shades ranging from light yellow to yellowish brown shades, although the color shade formed during the heat-curing treatment somewhat varies with the kind of fibre being applied, the kind of cross-linking agent being used, the kind and concentration of an alkaline substance, the heating temperature and the duration of the heat-curing step. And this discoloration may be somewhat eliminated by carrying out an after-bleaching operation on the fibrous material with hydrogen peroxide or the like. But the more intense the discoloration, the more difficult becomes the elimination. In addition, it is also difficult to carry out an after-bleaching operation on dyed fibrous material. These have been disturbing the industrialization of the heat-curing treatment method using the alkaline catalyst.
In order to inhibit the fibre yellowing occuring when the fibre material is heat-cured in the presence of the alkaline catalyst, there has hitherto been known a method using a boron-containing compound as disclosed in the U.S. Pat. No. 3,498,736. However, alkali metal borohydride which is a typical example of the boron-containing compounds, has drawbacks in that the chemical is high in cost, that the obtained whiteness of fibrous material is liable to vary with slight changes in the addition amount and in the conditions for heat-treatment, and that the chemical cannot be applied to dyed cloth because of its strong reduction bleaching properties. Also, the other typical example, borates, for example, borax or the like has a difficulty in operation control in factory production due to the fact that the preparation of the treating liquid becomes complicated because of its low solubility (only 1 gram of borax per 161 ml of water is dissolved), and that the whiteness of the fibrous material is liable to vary with the changes in the conditions for the heat treatment.